Labor has signalled it could support the Turnbull government's national energy guarantee but has serious doubts about promises on power price and emissions cuts.
Labor MPs were given a briefing on Tuesday night about the plan, which the government says will save households up to $115 a year between 2020 and 2030, while keeping the lights on and cutting emissions.
However, the MPs were told there was no specific modelling of the NEG's annual impact. Rather, the price-cut figures had been "extracted" from modelling of other similar proposals.
One MP said the estimated power bill saving had been described in the meeting as a "judgement call".
In question time on Wednesday, Labor leader Bill Shorten seized on a comment by Energy Security Board chair Kerry Schott, who said: "I don't think anybody can guarantee a price reduction."
Prime Minister Malcolm Turnbull told MPs he could guarantee "the authors of this recommendation know a lot more about energy and economics than anyone sitting opposite us today".
"What this will deliver is cheaper electricity, lower wholesale costs, savings for households and reliability - that's the triple bottom line."
Social Services Minister Christian Porter said $115 a year was "very significant" for many families.
Energy Minister Josh Frydenberg said the new mechanism would be modelled and that advice would be made public.
"It could be more than $115," he told Sky News.
Mr Turnbull said thousands of households, facing average power bills of between $2500 and $2700, had already seen reductions of about $400 by switching to the right price plan.
Mr Turnbull will need federal parliament's support to legislate part of the plan, while backing from the states - which are mostly Labor-held - will be needed for most of the plan to succeed.
Shadow treasurer Chris Bowen said Labor welcomed sensible and mature discussion based on evidence, but the government had produced nothing to back up its promises.
"We have policy on the run, we have an energy policy being put together with strings and band-aids," Mr Bowen said.
State Labor governments have expressed concern about the impact of the policy on their plans for more renewable energy, but there's no guarantee Liberal states will get on board.
NSW Liberal Premier Gladys Berejiklian wanted to see more detail before signing up to it.
"I'm not going to sign NSW up to anything unless it helps NSW citizens."
Tasmania's Energy Minister Guy Barnett said any federal policy would need to deliver lower prices, energy security and more renewable energy generation to get Tasmania's support.
"We aren't yet convinced by what we have heard and we need further detail on the federal government's plan," he said.
Energy ministers will meet in late November to discuss the policy, after which federal Labor is expected to formally decide whether it will support it.